Pot or crucible



I Patented Feb. 16,1926.

UNITED STATESvv PAT ARTHUR E. BnLLIs,

Nnw Yoan, N.

1,573,535 ENT OFFICE.

OF sPliINGFIELD, MASSACHUSETTS, AND CHARLES COLLINS, OF Y., ASSIGNORS, BY MESNE ASSIGNMENTS, T THE BELLIS HEAT TREATING COMPANY, 9F NEW HAVEN, CONNECTICUT, A... CORPORATION OF CON- NECTICUT ro'r on caU'crBLE.

Application led .October '18, 1920.` Serial No. 417,785.

To all 'whom t may concern.'

Be it known that we, ARTHUR E. BELLIS and CHARLEs 1S. COLLINS, citizens of the United States, and residents of Springfield,

5 in the State of Massachusetts, and borough' of Bronx, city, county, and State of New York, respectively, have invented certain new and usef l Improvements in Pots or Crucibles, of which the following is a specil0 lication. l

This invention relates'to pots or crucibles W for use in the 'art of heat treating metals and more particularly `toa pot or crucible adapted to contain a high temperature heat treating bath of salt solution, such forinstance as is shown and described in the .pat/ent of Arthur. E Bellis, No. 1,358,816'

granted November 16, 1920, orin the pendmg application of 4Charles S. Collins, Ser. No. 4o6,87o,.1ed August 3o, 1920.

Inl the art of heat treating yetalsthrough the medium of a salt bath sohition, it is the present practice when treating high-speed or alloy steels to use a graphite lcrucible foicontaining the salt bath components'. All salts, as for instance chlorides, borates, carl bonates, silicates, nitrates, etc., of sodium, barium, etc., which are liquid at 1,000 degrecs F. in the presence of a combining elemen\t,invariabl`y dissociate into'a basic oxide and an acid gas. The basic oxide reacts with the acid constituents in .the cruciblewall,1such as silicates, aluminates,'etc., while the acid gas which also attacks the alloy 35 metal being treated likewise combineswith the carbides, silicides or basic components of the crucible structure. These reactions in the wall of the crucible, more orle'ss violent, depending upon the proportions of acid 0 and basic refractory agents therein, cause a distress inthe wall structure 'so that graphitic vor amorphouscarbfon is freed or reeased and enters the bath solution, where it imay' at times seen floating on" the topI of thebath.

When the steel object to' be treated is immersed into the bath it comes into Contact *with this vcarbon which gathersl` u on the fsurfaces of the steel. Therefore,w en the v 59 'bath solution is heated to the high temperatureabove referred to, a rapid combination of the carbonwith the metal alloy occurs, thereby loweringthe melting temperature of the alloy steel being treated, which results in -blisters appearing upon `rthe surfaces of the metal. Y y In so far as we are -aware theJknown methods or processes as now employed in this art, are wholly inadequateto overcome the 'serious objection above referred to. It is, therefore, the primary purpose and object` of the present improvement toprovide a potl or crucible which is of such physical construction that it is rendered substantially immune to distressing reactions with the chemical constituents ofthe bath resulting from the dissociation of the bath components, 4so that the presence of free carbon" in thebath solution'will be wholly obviated.

More particularly our invention compre-k hends-a ,pot or` crucible, for use in the heat treatment of -.metals, preferably though not necessarily constructed of wrought iron or steel and containing in its physical structure a relatively low content of carbon, silica, alumina, or other binding 'agents either in the free or the combined form.

It is also a further object of our invention to provide a pot or crucible as above characterized which may be commercially4 produced atcompa'ratively small cost,`and used in connection with either of the crucible structures disclosed in our respective pend# ,ing applications above identied. A

With the above and other objects in view, the invention consists in the improved crucible having the novel structural characteristics which will be hereinafter more fully explained and vsubsequently incorporated in the subjoined claims.

Ourinvention may be better understood fromfreference tolthe accompanying drawing, whereinv we have illustrated a .crucible corresponding to the construction disclosed. in the said applicationof Charles S. Collins 95 and whichv represents a vertical sectional view A through the ot or crucible structure. Referring in detai to this drawing, 5 desig/ nates a furnace which may be of any approved or 'conventional form and as herein 100 .illustrated may be provided withv one or more openin s such as indicatedat' 6, through whic overflow or leakage may run o In' the embodiment of the invention here- 10Q in shown the potor crucible includes an` outer Wall or shell 8 which may be constructed or moulded of a metal alloy, graphite or any other suitable refractory material', more or less resistant to the attacks of oxidizing atmospheres. This outer or body wall of the pot extends through an opening 9 in the top wall of the furnace and is provided upon its upper end with an inwardly projecting annular flange 1() to rest upon the furnace Wall.

Within the body wall 8 the shell or lining 12 of wrought iron, steel or other metal valloy is arranged and preferably has a cross sectional contour conforming to the internal c shell both laterally and longitudinally in a downward direction.

1 Within the upper end of the shell 12 the vention which has given 'satisfactory results sealing ring 15 is arranged and has its annular body wall spaced from the wall of said shell, said ring being provided on one end with an outwardly projecting annular flange Ato seat upon the flange 13 of the shell. This ring which extends below the surface of. the bath solution roduces Aan annular sealed dead air space 1 which preventsthe entrance of exterior air into the shell 8 above the` bath solution and thus obiates oxidization of the shell at its upper en z As thus far described, we have merely' disclosed one desirable embodiment of the `in in practice,`but it will -be understood that the present improvement is not to be limited to any specific form`of\the crucible and a metal pot corres onding to the liner 12 may alone be used. of such a pot would be relatively .short due lto external oxidlization, and therefore we prefer to provide the external refractory protecting wall 8 as referred to in our respective ending applications.

Accor ingly, our present invention is to be understood as residing in the provision of a potA or container for fthe salt bath solution of .wrought iron, steel. or othermetal allo which contains inits ysilcal structure .A .pre erably less than 2% o carbon and also i 6'5 1800 degrees F. and above, Withoutcausi'ng preferably less than 2% -of silicates or alummates in either the'free or combined state. W'e have found in the actual use ofa pot or a distress in the wall structure of the pot.

bviously, however, the life pot results from the fact that the wall structure does not contain silica, alumina or other binding agents lin sufficient quantity to be disintegrated by chemical reactions as is the case when the attempt is made to use the ordinary graphite crucible for the high temperature treatment of metals. Such crucibles usually` contain approximately 60% of silicates or alumlinates.

In our present invention, however, these agents are not present in such quantity as would result in any appreciable reaction with the basic and acid components of the salt bath such as would be necessary in order to free or release the carbon from the pot wall. Thus by means of our invention it will be seen that Iin the treatment of high speed and alloy steels at high temperature the metal article at all times retains its high melting point so that there is no possibility of the surfaces of the .object when immersed in the bath being blistered by the combination of carbon with the alloy metal. It will therefore be manifest that a final product of very high quality may be ob-v tained. i

From the foregoing description, it is believed that the nature of our present improvement and its several advantageous features in actual practice will be fully appreciated. As hereinbefore observed we do not deem ourselves to be limited in so far as thisinvention is concerned to a pot or crucif ble of any particular size, form or construction, or to any specific material, the only essential requisite Iin order to 4procure the desired result being that the material from which the pot or Crucible is formed, Whatever its composition may be, shall contain comparatively limited quantities of carbon and silica, alumina or'other binding agents.

We claim: i

1. A potor crucible adapted to .contain a heat transfer bath consisting of a solution of chemical salts nu'etral to the metal to be treated and dissociating at high temperatures into a basic oxide and an acid gas, said pot or crucible having a Wall composed of mineral components, including Aminor quantities of carbon and basic impurities in ysuch predetermined proportions relative to the othercomponents thereof that said wall structure is essentially immune to chemical reaction with the basic oxide and acid gas :emanations from the bath solution whereby said bath solution is maintained free from impurities and neutral to the surface of the metal being treated.

2. A pot or Crucible for use in the heat treatment `of high speed tool steels adapted to contain a heat transfer bath `consisting of a solution of chemical salts neutral to the metal to be treated and dissociating at high temperatures into a basic oxide andan acid gas, the Crucible wall being of substantially uniform thickness throughout and formed from a ferrous metal alloy, said Wall structure .having combined with the other physical components thereof relatively small quantities of silicates, aluminates or other basic impurities whereby said Wall structure is rendered essentially immune to chemical reaction with the basic oxide and acid gas emanations from the bath solution and said solution maintained free from impurities and neutral to the surface of the metal being treated.

3. A pot or Crucible for use in the heat treatment of high speed tool steels adapted to contain a heat transfer bath consisting an acid gas, said pot orcrucible having a Wall structure formed from a ferrous metal alloy and containing, in combination with the other com onents, not more than two percent each o carbon, silicates, aluminates, or other basic impurities whereby said Wall structure is capable of withstanding atemperature Vof 1800o F. or greater Without releasing impurities from said wall structure into the bath solution and whereby said solution is maintained neutral to the sur face of the metal being treated.

In testimony that we claim the foregoing as our invention, We have signed our names hereunder.

ARTHUR E. BELLIS.. CHARLES S. COLLINS. 

